Since 1970, this laboratory has been investigating the vestibulo-ocular reflex (VOR): its behavior, underlying neurophysiology, and adaptive plasticity. The emphasis in this proposal is to explore further the capabilities for motor learning in the vestibular system of normal human beings in order to provide a firmer rationale for the exercise programs used to rehabilitate patients with vestibular disorders. Three problems in vestibular plasticity will be investigated in normal subjects. Project A concentrates on otolith-ocular responses (OOR), their interaction with canal and visual stimuli, and their plasticity. Most natural head motions contain components of translation as well as rotation; the former must be detected by the otoliths. Several methods to evaluate the OOR will be tried. One is to examine L-nystagmus: the eye movements that result from linear acceleration, but with careful control of the point of regard since the size of the compensatory responses to a translation depends upon viewing distance. By creating a visual- vestibular mismatch, as through magnifying goggles, we hope to demonstrate otolith-ocular plasticity. Then, different patterns of linear and angular motion will be combined (using eccentric rotation) and subjects tested to see if VOR plasticity learned in one behavioral context can be transferred to another. Project B addresses VOR linearity. The canals are nonlinear above a certain head speed. One side is completely inhibited, yet the VOR still remains linear. There must be a compensating, central (anti)nonlinearity that should be under adaptive control. This capability will be investigated. The findings may be of potential use in rehabilitation of patients with unilateral vestibular loss. Project C examines the problem of people who constantly switch from one magnification to another (bifocals, scuba divers, low-vision aids). Do they have two VOR gains and can they switch back and forth? Each of the proposed experiments bears on the issue of the degree to which VOR adaptation is context-specific. Any vestibular rehabilitation program must consider how well the learning acquired in an exercise program transfers to natural behavior.